1. Field of the Invention
The present invention relates to a semiconductor pressure sensor and a method for bonding a semiconductor chip to a metal diaphragm thereof, and more particulary to an accurate semiconductor pressure sensor suitable for the detection of high pressure and a bonding method therefor.
2. Description of the Prior Art
In many cases, there have been used pressure sensors, each being provided with such a pressure sensing diaphragm as to deform in response to the measured pressure. These pressure sensors sense the amount of deformation of the diaphragm by means of a strain gauge. In particular, for measuring high pressure, it is desired to use a metal diaphragm having pressure resistance. For example, Japanese examined patent publication No. Sho 58-5372 discloses a pressure sensor provided with a measuring portion composed of a metal diaphragm and a metal strain gauge bonded to the metal diaphragm. However, this metal strain gauge has a defect that the output sensitivity is low. This results in multistage amplification and noise removal being required, and accordingly the measuring circuit becomes complex.
Recently, pressure sensors, each being provided with a semiconductor strain gauge having a linear and high sensitive output have been noted. In each of these pressure detectors, a semiconductor chip itself composes a pressure receiving diaphragm (U.S. Pat. No. 3,858,150 for example). Therefore, these pressure sensors cannot be used for sensing high pressure.
For obtaining a pressure sensor durable against high pressure and having excellent output sensitivity, it has been thought of to combine the metal diaphragm with the semiconductor chip composing the semiconductor strain gauge. However, such a bonding structure to bond the semiconductor chip to the metal diaphragm with sufficient strenght has not been found as yet.